The present invention relates to a coating composition comprising a water continuous emulsion of a curable elastomeric polymer, an aqueous polyurethane dispersion, and an optional cure agent. Methods for making the coating composition are also taught. The present invention further relates to a cured coating product formed from the composition.
The use of airbags in motor vehicles has grown exponentially in recent years. Their use has expanded beyond frontal airbags for protection for the driver and passenger. Side airbags and inflatable curtains are now included in side compartments of vehicles for enhanced protection from side collisions or rollovers. This expanded use has placed new demands on the physical properties attributed to the airbags. In particular, improved air retention performance of airbags are desired to ensure the airbag remains inflated and maintains its integrity for an extended period of time upon deployment.
Typically, airbags are made from synthetic fibers, such as a polyamide (nylon) or polyester and coated with a polymeric film. The most common polymeric materials currently being used to coat airbag fabrics are based on silicones, as described for example in U.S. Pat. No. 6,037,279. The silicone coating primarily provides a thermal barrier on the airbags to protect the fabric from the high temperature burst associated with ignition of the gas upon deployment. The silicone coating also provides some gas retention properties for the deployed airbag. One option to meet the increasing demand for gas retention is to increase the thickness of the silicone coating. However, newer designs for airbags, and in particular side impact airbags and inflatable curtains for side compartments, require airbags to have a more compact design. This results in a need for lower coating weights on the airbag fabrics. Furthermore, next generation side and inflatable curtain airbags have a need to retain pressured air/gas for sufficient time to provide rollover protection for greater than 5 seconds. Current silicone based coatings are too permeable to air/gas, especially at lower coat weights, to provide sufficient gas retention in deployed side and curtain airbags. Thus, there is a need for a fabric coating composition, and methods of application, to provide coated fabrics with sufficient air/gas retention for use in the construction of airbags, and in particular side and curtain airbags.
The current airbag fabrics also requires the removal of unwanted sizing, protective oil after woven steps before application of the coating material. This is done by chemical scouring, washing, then drying of the scoured airbag fabrics. These steps are non-value added, labor-intensive, and costly. Also, residual moiture on the fabric surface can cause imperfections on the coated surface when a non-aqueous coating is applied. Thus, there exsits an additional need to develop a coating composition that can be applied directly over wet fabrics, provides good adhesion to the fabric, and dries to a uniform coating without imprefections.
One technique that has been reported to decrease coating weights and maintain low permeability performance of coated fabrics for use in airbags has been to use a two layered coating system, as disclosed for example in U.S. Pat. No. 6,177,365. The U.S. Pat. No. 6,177,365 teaches the application of a first layer to the fabric of a non-silicone material followed by the application of a silicone containing topcoat. U.S. Pat. No. 6,177,366 also teaches a two layer coating system for airbag fabrics where the first layer contains up to 30% of a silicone resin and the topcoat contains a silicone material. U.S. Pat. No. 6,239,046 teaches an airbags having a first coating layer of adhesive polyurethane and a second coating layer of an elastomeric polysiloxane.
Alternative coating compositions have been disclosed based on polyurethanes, such as in U.S. Pat. No. 5,110,666, or on polyurethane/polyacrylate dispersions as found in U.S. Pat. No. 6,169,043.
While the coating systems cited above represents advancements in airbag technology, a need still exists to provide improved compositions and techniques for coating fabrics for use in airbags. In particular, coating compositions that provide similar or improved permeability at lower coating weights and improved aging stability are desired. Furthermore, there is a need to provide coatings that eliminate the need for pre-treatment of the fabrics.
The present invention is directed to a curable coating composition comprising:
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C.;
(B) an aqueous polyurethane dispersion; and optionally,
(C) a cure agent.
Methods for making the curable coating compositions are also provided herein. The present invention is further directed to a cured coating composition comprising a reaction product of the above-described composition.